Transmission system



y 7, 1932. B. B. MINNIUM 1,859,103

' TRANSMISSION SYSTEM Filed Nov. 26, 1929 aywmtoz N 02 E-M IVN M 351;; 6 GHQ anew I Patented May 17, 1932 UNITED STATES P TE T OFFICE BYRON B. MINNIUM, or CHICAGO, rLLINoIs, ASSIG-NOR T STEWART WARNER coa PORATION, or RICHMOND, VIRGINIA, A CORPORATION or VIRGINIA I TRANSMISSION SYSTEM Application filed November 26, 1929. Serial No. 409,792. i

This invention relates to transmission circuits and "with particularity to a system employing thermionic devices as amplifiers, repeaters, etc.

As is well known in the art, because of the physical dimensions and arrangements of the structural elements usually employed in thermionic devices, there is an undesirable inherent coupling, which if not compensated 19 or balanced results in the generation of disturbing oscillations that are detrimental to proper operation of the amplifier. As a result also of the undesirable or distributed eX- ternal couplings between the electrodes means must befprovided for preventing such external couplings'from causing disturbing oscillations; Accordingly the invention has for its principal object to provide an amplifier or.repeater circuit'which is substantially free from disturbing oscillations.

A feature of "the invention relates to a transmission circuit employing thermionic amplifier or repeating devices, wherein changes in potential at one point in the circuit are prevented from causing undesirable changes of potential at another or other points in the circuit.

3 Another feature of the invention relates to an amplifier or repeater'circuit employing 0 a multi-electrode electron discharge device, wherein variations in the"0u,tput circuit tending to cause corresponding variations in the input circuit are themselves utilized to produce a corresponding balancing eflect on the input circuit whereby disturbing oscillations are prevented.

er with a novel form of balancing arrangement for preventing the generation of undesirable oscillations.

A still further feature of the'invention relat-es to an amplifier or repeater system employing a series of successive thermionic amplifier devices'having tuned input circuits and wherein means are provided for preve'nting the generation of undesirable oscillations by selecting a point between the grid and cathode of each device and applying tosaid point a potential derived from variations'in the output circuit of each device.

A still further feature of the'invention relates to a method of preventing the gen eration of undesirable oscillations in an electron discharge amplifier orrepeater by utilizing the inherent coupling between the anode and grid of the device, and also utiliz in the inherent coupling between the grid and cathode of the device in combination with a novel circuit arrangement employing a coil inductively connected between the out put circuit and a point intermediate the grid and cathode of the device. I

Other features and advantages of the invention not specifically'enumerated will be apparent after aconsideration of the followingdetail description and the appended claims. a 1 'VVhile the invention will be disclosed as applied to an amplifier circuit of the tuned type, it will be understood that'the invention in its broad aspects is capable of applica tion to any transmission circuit wherein multi-electrode electron discharge devices are "employed either for amplifying,"repeating, or for similar functions. P Accordingly, Figure 1 of the drawings shows one conventional type of tuned amplifier circuit employing. features of the inven-' tion. The amplifier devices illustrated in this circuit are of the'so-called indirectly heated or uni-potential-ca-thode type;

Fig. 2 illustrates the 'manner'of applying the inventive features to an amplifier cir cuit, using directly heated cathodes.

Referring more particularly to Fig. i of the drawings, numerals 1 and 2 representa source of variations such as electric waves known type, preferably it is of the so-called which are to be transmitted and amplified during transmission. These variations are impressed in the usual manner upon a coil 3 which forms the primary winding of a coupling transformer, the secondary winding 4 of which has the upper end connected directly to the grid 5 of an electron discharge device. This discharge device may be of well.

high vacuum type employing an electron emitting c'atho'ded, the controlling grid 5, and the anode or plate 7. If desired one or more'so-called shielding grids may'be'employed as is well known in the art. The lower. end of secondary winding is connected to ground-as shown, and a variable condenser 8 or other equivalent tuning element is connected across winding 4, preferably with the rotary or adjustable parts thereof connected to ground. For the purpose of rendering the cathode 6 emissive a suitable heater element 9isemployed. Supplementing the inherent electro-static coupling between the grid 5 and the plate 7 is a relatively small variable condenser 10, which is connected across the grid and plate asshown in the drawings. Another small variable condenser 11 isprovided externally of the amplifier tube to supplement the inherent electrostatic capacitybetweenthe grid 5 and the cathode 6.

* The operating potentialfor the anode 7 is derived from any suitable source of requisite potential represented schematicallg in the drawings by the numeral. 12. aid source of potential. is connected to the plate 7 throughja highfrequency choke coil 13.v

However, it is to be understood that the element 13 instead of being a choke coil may take the form of any impedance which is sufficiently high as compared with the output circuit of. the device to prevent the high frequency currents passing through the source 12. Connected in series between the cathode 6 and the anode 7 is a stopping condenser 14; and an inductance 15. Condenser 14: is preferably of sufliciently high capacity value to permit the flow of the signal modulations through the coil 15 and at the same time preventing the flow of direct current from the source 12 therethrough. Coil 15 forms the primary winding of an output transformer,- the secondary 16 of which leads to a succeeding amplifier stage if desired, or t0 any. suitable work circuits or device to be controlled. Inductively associated with the coil 15, and. preferably wound in the same direction as coil 15 is another coil. 17 which is connected between the cathode 6' and the grounded point P of the input circuit. .Inorder that'the proper bias may be imparted to the cathode 6 a suitable resistance 18 is connected. in series between the coil 17 and point Pas shownin the drawings,.and a bypass condenser '19 is connected acrossresistance'18. The relative direction of windings in coils 15,16 and 17 may be as desired as long as they are so poled that the winding 17 feeds current to the point P of the input circuit in a direction to oppose that tending to flow through the tube from plate to grid.

As a result of the circuit arrangement disclosed in Fig. 1, the same is substantially free from undesirable oscillations partly because of the shunt-feed method of supplying voltage to the plate 7. This latter method of feeding potential is particularly advantageous where a plurality of successive amplifier devices or stages are employed, since it reduces the efiective coupling between such stages resulting from the use of a common applied to grid 5 in accordance with the incoming wave. These varlations in plate current flow through the primary winding. 15' of'the output transformer and cause a corresponding alternating voltage to be generated between the anode 7 and the cathode 6. This voltage variation between anode and cathode causes a flow of current through the inherent capacity between theanode 7 and grid 5, and consequently to the upper. end of the. coil4. This ordinarily results in the generation of disturbing oscillations. For the purpose of preventing these oscillations the coil 17 which is inductively related tocoil 15 is so adjusted either as to number of turns degree of coupling, etc. that alike quantity of current is fed to the 1 lower end of the input coil. 4 through the inherent capacity between grid 5 and cathode 6. When the effects of these two opposing currents are equal they of course annul each other.

In order to facilitate the adjustment. of the balance, the coils 15 and 17 if desired, may be maintained in fixed relation and the condensers 10 and 11 adjusted to the point where the circuit is stable and then these condensers may be locked in adjusted position. It is evident that if desired the coils 15' and 17 may be adjustable as regards the number of inductively related turns, as well as in their relative inductive positions and either one or both of condensers '10 andll may be adjustable. In practice however, it is simpler to adjust the condenserll to effect the balance of the circuit.

As shown in Fig.- 1 theamplified impulses which are repeated into the secondary16 may be fed to succeeding amplifier stages schematically represented by the numeral 20, all these latter stages being preferably identical with the stage already described in. detail.-

1A suitable work circuit represented schematically by the numeral 21 is connected to the last stage 20in any well known manner.

Fig. 2 of the drawings shows the manner in which the balancing arrangements according to the invention are applied to electron discharge devices employing directly heated cathodes. Elements shown in Fig. 2 corresponding to similar elements of Figure 1 bear the same designation numerals, and their function is identical with that already described. However in Fig. 2, inasmuch as the filament cathode 20 is not of the uni-potential type, but has a drop of potential therethrough, it is necessary to provide a path for the filament heating current from the source 21. In order to supply this filament current and at the same time not disturb the balance, the coil 17 of Figure 1 is replaced by two parallel coils 22 and 23, both of which are inductively related to the output coil 15 as already described in connection with coil 17. The method of operation of the circuit of Fig. 2 is substantially the same as that described in connection with Figure 1.

While the invention is particularly well suited to transmission circuits for amplifying or repeating high frequency waves, it will be understood that corresponding advantages may be derived in any system wherein electric waves of any frequency are utilized, and it is not necessary to achieve the object balancing coils inductively related to said output inductance, each coil of said pair being connected to a leg of said filament, and a source of filament heating .current connected in parallel with said coils. 4'

2. An amplifier system according to claim 1 in which the output inductance is connected to the anode through a'condenser and the anode potential is applied in shunt to said output inductance through a relatively high impedance.

3. In an amplifier system the combination of an electron discharge device having an electron emitting cathode, a control grid and an anode, an input inductance having one end connected to said grid, an output inductance connected between said anode and cathode, one end of said inductance being directly connected to said cathode, another inductance inductively coupled .to said output inductance having one end directly connected to said cathode and the other end connected in series with said input inductance. V

In testimony whereof I have hereunto set my hand on this 16th day of November A. D., 1929. BYRON B. MINNIUM.

of the invention that the respective input and 2 output circuits be tuned to any particular frequency or frequencies. Furthermore the potential for the plate or anode circuits may be applied through any high impedance. For example, a circuit anti-resonant with respect to the frequencies encountered in the transmission circuit proper may be employed.

lVhile the invention is illustrated in a system for preventing oscillation in the input circuit of an amplifier it will be understood that the invention, in its broad aspects, is capable of application to any repeater circuit wherein it is necessary to prevent the flow of energy in a direction opposite to that of the intended repeater action. Likewise the invention provides within its scope a method of )reventing oscillation either in the grid an or anode circuits of an electron discharge device.

Other changes and modifications may be made in the circuits and apparatus without departing from the spirit and scope of the invention.

What is claimed is:

1. In an amplifier system employing multi-electrode electron discharge devices, means for suppressing undesirable oscillations due to inter-electrode capacities including an input inductance connected to the grid of said device, a filamentary cathode for said device, an output inductance having one end connected to the anode of said device, the oppo site end of said output inductance being directly connected to said cathode, a pair of 

